The remaining capacity of a battery can be estimated on the basis of the SOC (State Of Charge), which is the ratio of the remaining charge amount to the fully charged state of the battery. The State Of Charge (SOC) is also referred to as a charge state and is also referred to as a remaining capacity (SOC).
Generally, in the estimation of a remaining capacity (SOC) of a lithium-ion battery, a nickel-hydrogen battery, etc., the Open Circuit Voltage (OCV) is estimated from the Closed Circuit Voltage (CCV). Thereafter, by referring to map data of the SOC-OCV characteristic, which results from associating the remaining capacity (SOC) with the Open Circuit Voltage (OCV), the remaining capacity (SOC) is estimated from the Open Circuit Voltage (OCV).
When the SOC-OCV characteristic is obtained, the value of the Open Circuit Voltage (OCV) of the battery is obtained from for example the voltage value of the battery at a time point when three hours have elapsed after halting the power supply at the temperature of twenty five degrees. However, because a lithium-ion battery etc. that uses an SiO negative electrode does not have the polarization resolved completely even three hours after the halt of the power supply, the obtained value is not an accurate Open Circuit Voltage (OCV).
Accordingly, in a battery in which the polarization is of a large scale and it takes a long time to resolve it, a charging-side SOC-OCV characteristic 81, which is measured during charging, and a discharging-side SOC-OCV characteristic 82, which is measured during discharging, greatly differ from each other in hysteresis, making it difficult to estimate the remaining capacity (SOC) from the Open Circuit Voltage (OCV) in a manner shown in FIG. 8.
Against this background, the estimation of a remaining capacity (SOC) on the basis of an SOC-CCV characteristic resulting from associating the Closed Circuit Voltage (CCV) with the remaining capacity (SOC) is being discussed. Although SOC-CCV characteristics differ between when the battery is being charged and when the battery is being discharged, Patent document 1 below and other documents describe a technique of estimating a remaining capacity (SOC) by using the SOC-CCV characteristic.
Patent Document 1 describes a charge state management device, for a battery that is charged and discharged repeatedly and randomly, that refers to the SOC-CCV characteristic on the basis of the battery voltage during discharging so as to obtain the remaining capacity SOCx, and outputs the remaining capacity SOCx as the current remaining capacity SOC when the remaining capacity SOCx is smaller than a minimum remaining capacity SOCmin stored in the storage unit in order to update the minimum remaining capacity SOCmin by referring to the remaining capacity SOC.